This aluminum frame extrusion is used to make the sash (front frame) on a Hehr Hall-Mark 12 window. This profile is used to make the top of the frame only. A different profile VTS-2143A is used to make the side and bottom sections of the frame. You will need to miter and weld corners.
Comes 47" long so you will likely need only one of these to make a single sash.
Used on Airstreams from 1961 to 1965. Also seen on some other trailers.
Mill finish can be polished.